This invention relates to a communication apparatus performing communication via a telephone line, and particularly relates to a communication apparatus including a line connection terminal having at least two contacts to which a telephone line is connected, and a telephone connection terminal having at least two contacts to which a telephone set is connected.
In an example of conventional communication apparatuses, a CML (Connect Modem to Line) relay and a loop current detection circuit are provided. The CML relay switchably connects a line connection terminal to one of a telephone connection terminal and a modem unit. The loop current detection circuit detects a current flowing from the CML relay to the modem unit when the line connection terminal is connected to the modem unit via the CML relay. According to this example, it may be determined that a telephone set is improperly connected to the line connection terminal when the loop current detection circuit detects no current.